MXPA06007747A - Transmission shift control method. - Google Patents

Abstract

A method is provided for shifting a powershift transmission in a vehicle having an engine controlled by an electronic engine control unit and a powershift transmission controlled by an electronic transmission control unit. During a shift the powershift transmission has an off-going clutch and an on-coming clutch. The method includes determining a Predicted Off Slip Pressure for the off-going clutch and determining a Predicted On Slip Pressure for the on-coming clutch, both as a function of engine load. The Predicted Off Slip Pressure is a pressure at which the off-going clutch would start to slip, and the Predicted On Slip Pressure is a pressure at which the on-coming clutch would start to transmit torque. Thereafter, the method includes rapidly reducing off-going clutch pressure, P-off, to a pressure which is slightly higher than the Predicted Off Slip Pressure, and rapidly increasing on-coming clutch pressure P-on to a pressure that is slightly lower than the Predicted On Slip Press ure. Then, the method includes gradually decreasing P-off and gradually increasing P-on until slipping of the off-going clutch is detected, and gradually and more slowly decreasing P-off and gradually more slowly increasing P-on until the oncoming clutch begins to carry torque previously carried by the off-going clutch. Finally, the method includes more rapidly decreasing P-off to reservoir pressure, and more rapidly increasing P-on to a full on pressure.

Description

TRANSMISSION CHANGE CONTROL METHOD Background The present invention relates to a method for changing a power shift transmission.

The conventional power shift transmissions use solenoid controlled valves to control the pressure in each clutch, and such transmission rates change by disengaging one or more clutches while simultaneously engaging one or more clutches. Such transmissions also depend on a signal that is representative of the motor load to determine the pressure applied to the incoming clutches.

The smooth gear change is normally controlled by engaging the incoming clutches at low pressure. The amount of pressure required depends on the load that is transmitted by the transmission to the drive wheels. If the gear pressure is too low, the vehicle may lose speed during the change. If the gear pressure is too high, the change can be very aggressive and rough.

Several problems can occur with this conventional type of system. For example, sometimes the incoming clutch piston will not be able to move enough to start the gear, even when the outgoing clutch has been disengaged. Under load this may cause the vehicle to lose speed during the change. Even when the solenoid valve is sufficiently open to provide the correct pressure, the subsequent incoming clutch may not engage and can not transmit the torsional force.

Another problem is that the motor load signal can be misleading. For example, in agricultural tractor applications, there are conditions where much of the engine load can be used to power a hydraulic pump or power take-off (PTO) attachments. This can cause a rough change quality because the incoming clutch pressure is commanded at high pressure when instead it should have been commanded to low because really only a small amount of the motor power was being transmitted to the drive wheels .

A method for reducing the problem of the incoming clutch that is not being filled is described in U.S. Patent No. 5,580,332 issued 1996 to Mitchell et al. In this method, the actual clutch filling time is determined during each change. Depending on whether the clutch is filled sooner than expected or later than expected, the fill time that is used for the next clutch gear can be adjusted. The filling time is determined by bringing the clutch protruding down to a lower stable valve, while the incoming clutch is brought up to the filling pressure, then looking for the point in time in which the outgoing clutch slides or the proportion of the speed of the torque converter changes.

A method to control the change of the transmissions of change and overcome both deficiencies is described in the patent of the United States of America No. 6,193,630 and in the patent of the United States of America No. 6,435,049 both assigned to the transferor of this application . In this method, the first step in a change is to bring a clutch protruding down under pressure until the slip is detected. The slip is caused purely by the load on the vehicle, not by the incoming clutch to which the pressure is rising. The protruding clutch is then maintained in a light slip condition while the incoming clutches are being filled and other exchanges of intermediate clutches are effected. Finally, the last exchange is made between this outgoing clutch and the final incoming clutch.

With this method, under some conditions where there is very little load on the drive train, it may take a considerable amount of time to detect the slip, so it causes a delay in time since when the operator orders a change by moving a lever of change and until the change really happens. Such delays are hated by operators because they give them the impression that they are not in control. Also with this method, only after a slip is detected in the outgoing clutch, the incoming clutch is brought to pressure. This additionally delays the completion of the current change.

Another disadvantage of this method is that the first slip detection always results in the vehicle slowing down. During a change up, it is not desirable to feel the vehicle slow down before it finally accelerates.

Synthesis Therefore, an object of this invention is to provide a method for smoothly changing a shift transmission which does not cause the vehicle to lose speed during the shift.

A further object of the invention is to provide such a method for the smooth change of a shift transmission which does not channel a rough change quality due to a misleading motor load signal.

These and other objects are achieved by the present invention, wherein and when a change is ordered, both of the outgoing and incoming clutches are ordered at pressures that are a function of the motor load signal. The purpose of this step is to quickly get the outgoing clutch to the pressure that is slightly higher than what would be expected at the beginning of the slip. In the same way, the incoming clutch is quickly brought to a pressure that is slightly lower than what it can take to carry the engine load. From that starting point, the protruding clutch is inclined downward under pressure while, simultaneously, the incoming clutch is being tilted upward.

The speed sensors are used in the transmission input change, in the transmission output change, and an internal transmission component so that the system can determine when any of the clutches is sliding.

The inclination of the output clutch and the input clutch continues until the slip in the output clutch is detected.

In the case of a downward shift, the slip is caused by both the external load on the vehicle as well as the torsional force that is produced by the input clutch. When the slip is detected, the pressure in both clutches is stabilized and slowly tilted so that a smooth transition can be made from one clutch to the other.

In the case of an upshift, the tilt of the output clutch low and the upstream clutch continues until the positive tilt is detected in the output clutch. In this case, the torsional force produced by the input clutch must overcome both the external load on the vehicle and the torque which is carried out by the output clutch. Similar to the downward shift, when the positive slip is detected, the pressures on both clutches are stabilized and slowly tilted so that a smooth transition can be made.

In the above-described change only one clutch is engaged and a clutch is disengaged. This control strategy is also useful in changes that require multiple clutch exchanges. The exchange of the other pairs of clutches may be ordered after the slip is detected in the first output clutch and before the last input clutch is brought under pressure.

Brief Description of the Drawings Fig. 1 is a schematic block diagram of a transmission control system according to the present invention; Figure 2 is a schematic diagram of the transmission of Figure 1; Fig. 3 is a logic flow diagram illustrating an algorithm executed by the transmission controller of Fig. 1; Fig. 4 is a logic flow diagram illustrating an algorithm represented by step 106 of Fig. 1; Figures 5A, 5B and 4C contain a pseudo code program that lists a subroutine performed by the algorithm represented by Figure 4; Fig. 6 is a time diagram of the clutch pressure commands and throttle valve of the engine according to the present invention; and Figure 7 is a timing diagram of the clutch pressure commands according to a transmission control system of the prior art.

Detailed description Figure 1 is a schematic block diagram of a microprocessor-based transmission control system 10 to which it is applicable in the present invention. A vehicle power train includes a motor 12 which is controlled by an electronic motor control unit 14, which drives a power shift transmission (PST) 16 through the input shaft '13. The transmission 16 has a counter shaft 15, and an output shaft 18 which is connected to the drive wheels (not shown). The power shift transmission 16 includes a set of pressure operated control elements or clutches 20 which are controlled by a corresponding set of proportional control valves operated by solenoid 22. The transmission 16 may be a transmission as described in FIG. U.S. Patent No. 5,011,465 issued April 30, 1991 to Jeffries et al., and assigned to the assignor of this application. The valves 22 may be two-stage electro-hydraulic valves as described in U.S. Patent No. 4,741,364 issued May 3, 1988 to Stoss et al. And assigned to the assignor of this application.

The power shift transmission 16 is controlled by a transmission control unit 24, a rest arm control unit 26 which receives and interprets the commands of the shift lever of the shift command lever unit 28. The shift command lever unit 281 is preferably a conventional shift command lever unit used in the production of John Deere tractors, and includes a gear change lever 29. Such a shift command lever unit is described in the patent of the United States of America No. 5,406,860 granted on April 18, 1995 to Easton and others, and assigned to the transferor of this application. An display unit 30 may display information that relates to the system 10. The transmission control unit 24 and the rest arm control unit 26 preferably are electronic control units based on microprocessors.

The manual control is achieved by means of a gear shift command lever unit controlled by the operator 28. The unit 28 provides signals representing the position of the lever 29 to the arm rest control unit 26. The unit Rest arm control 26 sends change command information to the transmission control unit 24 by means of a vehicle communication bus 30.

A clutch gear sensor 32 and a clutch disengagement switch 34 provide signals representing the position of a clutch pedal 36. The engine control unit 14 receives signals from an engine speed sensor 38, as well as from other sensors (not shown) which allow the engine control unit to transmit load information to the motor on the vehicle communication bus 30. The transmission controller 24 receives signals from a 40 axis speed sensor, a velocity sensor counter shaft 42 which senses the speed of an intermediate or counter shaft 15 which is inside the transmission 16, and a transmission oil temperature sensor 44. The transmission controller 24 sends the information of the speed of the transmission. wheel (calculated from the axle speed based on the size of the wheel), and from the oil temperature to the merchandiser 34 by means of the communication bus of the vehicle 30. It informs The speed of the intermediate shaft is used only for control purposes and is not displayed under normal operating conditions.

The transmission control unit 24 includes a commercially available microprocessor which supplies control signals to a set of valve drives (not shown) which provide modulated duty cycle pulse width modulated voltage control signals to the valves 22. The transmission control unit 24 generates control signals as a function of several inputs perceived and determined by the operator in order to achieve a desired pressure in the clutches and thereby control the changes of the transmission 16 in a desired manner. . As best seen in Figure 2, the transmission 16 includes several changes, gears and clutches, which include the clutches AB, BC, CC, DC, Cl, C2, C3, C4 and CR. For example, when a shift range 5F to 4F is carried out the clutch AB is disengaged while the clutch BC is engaged, a clutch C4 is disengaged while the clutch Cl is engaged.

The transmission controller 24 executes a known production master circuit algorithm (not shown) which controls the hydraulic pressures that vary with time which are applied to the various transmission clutch members. According to the present invention, the controller also executes an algorithm represented by FIGS. 3 and 4. The conversion of the flow charts of FIGS. 3 and 4 into a standard language for implementing the algorithm described by the flow chart in a digital computer or a microprocessor, may be evident to one with ordinary skill in the art.

Figure 3 illustrates how this method is implemented by an algorithm 100 executed by the transmission controller based on microcomputer 24. This algorithm 100 is preferably executed at least once every ten milliseconds by a type of task manager operating on time. real and that runs in the transmission driver 24.

Before the algorithm 100 is run, the controller 24 may already have determined or calculated 1) what change it is desired to be executed, and 2) an array of values which represent the current time in the change for each clutch element. The algorithms 100 and 200 determine the clutch pressure values. After the algorithms 100 and 200 are run, the main circuit algorithm applies the desired pressures to the particular clutches involved in the change that is executed.

Referring now to Figure 3, the algorithm begins at step 102. At step 104 the algorithm is supplied with a pointer to an observation table (not shown) containing the known change parameters for the particular change that is ordered, in this case, for example, a change of rank 5F to 4F. Then in step 106 the algorithm obtains an array of predetermined change time values for each clutch element. Step 108 represents a start of the circuit for each transmission clutch element. The circuit of the main clutch element which begins in step 108 is executed once for each transmission clutch element.

The Processing of the Observation Table is performed in step 110. This processing uses the real time value of the clutch and the desired change to adjust an observation table pointer to the command step that must be executed for the clutch element. of transmission. Each command step contains the following three components. First, the time during the change when this command step must be executed. This time can be an absolute time, or it can be one related to a previous command step. Second, either a pressure command or a special instruction. Third, an inclination. The tilt input is used for open circuit changes that are not subject to this patent application.

Step 112 determines whether or not the observation table pointer indicates that the clutch slip logic must be effected for this transmission clutch element. If yes, then step 114 executes a function or subroutine of clutch slip 200 which calculates a clutch pressure according to a subroutine or function described in greater detail with respect to figure 4. If it is not, the algorithm proceeds to step 116 and the clutch pressures are determined in an open circuit manner known as was done in a prior production transmission controller.

Referring now to Figure 4, the clutch slip routine 200 starts a step 202. Then, in step 204 the subroutine obtains speed data from the sensor motor 38, the motor load data from the motor controller 14, the change rate data of either the sensor 40 or 42, and the gear ratio data of an axis velocity versus the current gear observation table (not shown).

If it is the first time that the subroutine 200 is being input to this particular transmission clutch element for this particular change, then the routine is directed to step 212, or to step 214.

Step 212 calculates the slip pressure that is predicted as a function of the motor load of step 204. More particularly, step 212 is related to the amount of torque from the motor passing through transmission 16 to the slip pressure according to the linear equation: Motor torsion force (Nm) = slip pressure (kPa) * m + b, where the tilt m and the b intercept are empirically found. The predicted slip pressure is then calculated by using the above equation, solved for the slip pressure. Therefore, the predicted slip pressure (kPa) = (motor torque force -b) / m. Preferably, the empirically determined intercept b is made in relation to the value of the calibrated filling pressure for the transmission clutch element by subtracting the product from the calibrated filling pressure and the inclination m. Therefore, the developed equation of experimental data can be applied to all tractors to which the method or system described in this application apply.

Next, step 214 determines whether the algorithm is in a fast tilt down phase. Each clutch member has an associated computation program counter (not shown) which indicates the number of steps through the clutch slip subroutine 200 since the change began. Whether or not the subroutine executes a low-tilt-fast phase or proceeds to a gradual down-tilt phase is based solely on the value of this against circuit. If the counter-circuit is less than some value, for example 6, the subroutine proceeds to step 216 and causes a rapid low tilt in the output clutch pressure. Step 216 calculates a desired pressure value as a function of the predicted pressure slip determined in step 212 and the number of steps through subroutine 200, wherein the pressure slip determined in step 212 is essentially at a pressure target for the initial rapid tilt low. For example, the following equation can be used to calculate the pressure ordered during this phase of rapid low tilt: Ordered Pressure = Previous Pressure Output - (Objective Change * 2/3).

In the above equation, the Target Change is the difference between the Previous Pressure Output and the predicted slip from step 212, where the previous pressure output is initialized to the full system pressure. After step 216, subroutine 200 and algorithm 100 terminate and, in a known manner, controller 24 applies the ordered pressure to the appropriate clutch member of transmission 16.

The intention of the fast downward tilt phase is to decrease the clutch pressure quickly at a pressure that is slightly above where the engine load signal indicates the clutch element can just begin to slip. The method is used to minimize the total execution time of the algorithm. The profile of the pressure command during the fast downward tilt phase is empirically determined to minimize the short throw in the pressure.

Returning to step 214, if the algorithm is not in a phase tilt rapidly down (as when the phase tilt down quickly has been completed), then step 214 directs the subroutine to step 218 which operates to cause the clutch pressure is tilted down more gradually, such as by a fixed amount each time through the routine, for example 2kPa, while the system attempts to detect the slip in the clutch. The slip is defined as the relative movement between the clutch plates (not shown). Step 218 calculates the slip ratio value using this equation: Slip proportion = (shaft speed * gear ratio) / motor speed. The shaft speed can be the speed of the output shaft at an intermediate transmission speed, depending on which transmission clutch is being slid. The gear ratio is determined from the current gear in which it is transmitted at the start of the gearbox. Preferably, the slip ratio is calculated with an accuracy of 0.1%.

Then, step 220 applies a noise rejection or filtering process to the Slip Proportion value of step 218 and calculates a Current Slip based on the filtered slip ratio of noise. Step 220 preferably includes a digital average filter N / (N + 1) and digital logic which operates to verify the direction of the slip (positive or negative) and compare the current slip value with the value of the previous step through the algorithm . N is an integral number that represents the average filter size. Preferably in the present application, N is 0 (for example it means no average) for the clutches 20 of the transmission 16. However, that some other number will be able to work in other applications.

The functions of step 220 are preferably effected by the pseudo code disclosed in Figures 5A to 5C. Therefore, this pseudo code calculates the slip (of the incoming or outgoing clutch) by comparing the input speed to the speed of the output shaft 18 or the counter shaft 15, as appropriate. Normally, the input speed may be the motor speed. The averaging of the calculated value is done through the multiplier N as previously described. This function sets the new average value of the clutch slip.

The pseudo code uses a parameter Ulntl6_T (no signature, 16-bit) that represents the input speed and a pointer to store data associated with the particular clutch. The pseudo code exits or returns an Ulnt8_T value (without signature, 8-bit) that indicates the direction of the slip. The positive slip is defined as the output speed that is greater than the input speed, the negative slip is when the input speed is higher than the output speed.

If the negative slip is being detected, a slip ratio of 0.980 may correspond to a real slip of 2.0%. If the negative slip is detected, a slip ratio of 1.020 may correspond to a real slip of 2.0%.

Step 222 determines whether the slip is detected or not. For example, a valid slip is detected if the actual slip is greater in magnitude than the previous slip value, in the same direction, and is greater than a Slip Detection threshold, preferably 3.0%. Additionally, a control parameter, preferably 2, is stored in the memory for each clutch element to adjust how many valid slip events must occur before the slip is detected. These values can be determined empirically, and other values may be preferable in other applications.

If the slip is not detected in step 222, then step 228 calculates a desired Pressure value by subtracting a fixed amount from the previous pressure command.

If the slip is detected in step 222, then step 224 is incremented to the same time value for each time value in the arrangement of current shift time values for each clutch element.

Preferably, the time value for each clutch element is likewise adjusted to an alignment time + TWAKEJYIAX where TWAKE_MAX is a constant stored in memory, such as 500 milliseconds. This has the effect of aligning all of the desired clutch pressure commands in real time. The alignment time is chosen to be large enough to allow sufficient time for slip detection in the worst conditions. This process can be described as "skipping ahead of time" in the change, since the next time the main circuit is executed, the command step corresponding to a time = alignment time + TWAKE_MAX may be the command step executed for each clutch element.

Then step 226 calculates a Desired Pressure value by subtracting a fixed amount from the previous pressure command.

Following either step 226 or 228 the algorithm ends in step 230.

Referring now to figure 6, when a change to low is ordered in time TO, both the output clutch pressure P-off and the inlet clutch pressure P-on are ordered at pressures that are a function of the motor load (which is derived from a fuel signal from the engine control unit 14). More particularly, the output clutch pressure P-off is rapidly reduced to a pressure at which it is slightly higher than a pressure at which it may begin to slip. Also, the inlet clutch pressure P-on is rapidly increased to a pressure that is slightly lower than a pressure at which the engine load can carry.

From a starting point, the output clutch pressure P-off is gradually decreased or tilted down while the input clutch pressure P-on is gradually increased or tilted upward. While P-off and P-on are being modified, the speed sensors 40, 42 and 44 monitor the speed of the transmission input shaft 13, a transmission output shaft 18, and an intermediate or counter axis 15 for determine when any of the clutches is sliding. The P-off and P-on pressures continue to be modified as described until the slip of the output clutch is detected.

In the case of the downward shift of Figure 2, the slip is caused by both the external load on the vehicle as well as the torque that is produced by the input clutch. When the slip of the output clutch is detected, both P-off and P-on pressures are stabilized and more slowly modified so that the torque is more smoothly transferred from the output clutch to the input clutch.

In the case of an upshift, the P-off decreases and the P-on increases until the positive slip of the output clutch is detected. In this case, the torque produced by the input clutch must overcome both the external load on the vehicle as well as the torque that is carried out by the output clutch. Similar to the shift down, when the positive slip is detected, both P-off and P-on pressures are stabilized and slowly tilted so that a smooth transition can be made. , Instead of using an open-loop control of the clutch pressure after the slip is detected as in Figure 6, the closed-loop control can be used where the system can detect an inlet clutch lock and also provides clutch control to achieve a closure in the desired time interval. The change can be completed until the closing of the input clutch, and the output clutch can then be completely released and the input clutch brought up to full pressure as in figure 7.

An additional feature which can be used in this change control method is to change the speed control of the throttle valve of the engine starting with the time when the slip of the output clutch is first detected. This additionally improves the smoothness of the change. By changing the throttle valve speed command during the shift, the shift transmissions are described in U.S. Patent No. 6,254,509. The present invention can determine the exact time event when the change really started which helps in taking the time the throttle valve command changed to the current change.

The above description relates to a change where only one clutch is engaged and one clutch is disengaged. However, the method of the present invention can also be used to change which require multiple clutch exchanges. The exchange of the other pairs of clutches can be ordered after the slip is detected in the first output clutch and before the last input clutch is brought to the pressure.

Figure 7 illustrates a change in accordance with prior art methods described in the aforementioned patents of the United States of America Nos. 6,193,630 and 6,435,049. In this method, when a change begins a time ti the output clutch pressure is rapidly reduced and then gradually reduced until the slip is detected at time t2. The output clutch pressure is then maintained in a light slip condition up to time t3 while the input clutch is filled and the exchange of the other intermediate clutches (not shown) is effected. Finally, the last exchange is made at time t3 when the output clutch is additionally and rapidly depressurized and the input clutch is completely pressurized.

Because the output clutch will not be able to slide until the input clutch is full and carries the torque, the method of the present invention avoids the problem of the input clutch which is now fully pressurized and engaged when the output clutch is released.

Because the output clutch is tilted down and then maintained at a pressure at which the slip occurred, the method of the present invention prevents the rough change that may occur when the load signal was misleading and the incoming clutch is engaged. at a very high pressure. Keeping the output clutch at a pressure where the slippage starts preventing the inlet clutch from engaging very quickly and causing a very hard, aggressive shift.

The change control method of the present invention is especially effective in making gentle downward changes. It is better to transition to the next gear by slowly releasing the output clutch instead of bringing the input clutch to a low pressure while fully releasing the output clutch.

With this new method of change control, because the input clutches are full and carry torsional force when the slip is detected, the slip is detected faster when it is under lower load conditions and the separation between the ordering operator a change and the change that really happens is reduced. Also, the operator's expectations for an upward shift are met. The vehicle only increases speed during an upshift, initially it does not decrease speed.

A signal representing the initial slip of the output clutch slip provides a good indication that the change has started and such a signal can be used to synchronize the choke valve command changes to the engine. Such command changes from the throttle valve to the engine during the change can additionally improve the smoothness of the change.

Compared with the method described in U.S. Patent No. 5,580,332, this new method of change of the present invention reacts to the detection of a clutch slip, and not only uses this information to adjust the filling time the next time the clutch is engaged. The clutch slip is determined while the output clutch pressure is tilting down and the inlet clutch pressure is tilting upward, not by placing the output clutch at a constant low pressure and the inlet clutch at a pressure. constant bottom filling.

Although the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations may be apparent to those skilled in the art in light of the foregoing description. Therefore, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.

Claims (5)

1. A method for changing a power shift transmission having a protruding clutch and an incoming clutch, the method comprises: when a change is commanded, quickly reduce the outgoing clutch pressure, P-off, to a pressure which is slightly higher than a pressure (Predicted Outward Release Pressure) at which the outgoing clutch will start a deslis, and rapidly increasing the inlet clutch pressure P-on at a pressure that slightly lower than a pressure (Predicted Entry Exit Pressure) in the incoming clutch will transmit the torque; then, gradually decrease P-Off and gradually increase P-on until the outgoing clutch slip is detected; then, gradually and more slowly decrease P-off and gradually more slowly increase P-on until the incoming clutch begins to carry the force or torque previously carried by the outgoing clutch; Y more quickly decrease P-off to a reservoir pressure, and faster increase P-on to a full inlet pressure.

2. The method of change as claimed in clause 1 characterized in that it also determines the predicted inlet pressure as a function of the engine load.

3. The method of change as claimed in clause 1 characterized in that it includes determining the engine load from a vehicle engine control unit.

4. In a vehicle having a motor controlled by an electronic motor control unit and a power shift transmission by an electronic transmission control unit, during a shift of the power shift transmission having an outgoing clutch and an incoming clutch , a method to change the transmission of power shift in response to an orderly change, the method comprises: determining a predicted outgoing slip pressure for the outgoing clutch as a function of the engine load, the outgoing outgoing pressure predicted to be a pressure at which the outgoing clutch will begin to slide determining a predicted incoming deflection pressure for the incoming clutch as a function of the engine load, the predicted clutch pressure being a pressure at which the incoming clutch will begin to transmit the torsional force; Quickly reduce the outgoing clutch pressure, P-off at a pressure which is slightly higher than the predicted outgoing relief pressure, and quickly increase the incoming clutch pressure P-on to a pressure that is slightly lower than the pressure of incoming descending predicted; then, gradually decrease P-off and gradually increase P-on until the outgoing clutch slip is detected; then, gradually and more slowly decrease P-off and gradually more slowly increase P-on until the incoming clutch begins to bear the torque previously carried by the outgoing clutch; Y then more quickly decrease P-off to a reservoir pressure and more rapidly increase P-on to a full incoming pressure.

5. The method of change as claimed in clause 1, characterized in that it also comprises: determining a motor load of the motor control unit. SUMMARY A method for changing a power shift transmission in a vehicle having a motor controlled by an electronic motor control unit and a power shift transmission controlled by an electronic transmission control unit is provided. During a shift of the power shift transmission you have a protruding clutch and an incoming clutch. The method includes determining a predetermined outgoing relief pressure for the outgoing clutch and determining a predicted incoming deflection pressure for the incoming clutch, both as a function of the engine load. The predefined outflow pressure is a pressure at which the outgoing clutch will begin to slide, and the predicted incoming draft pressure is a pressure at which the incoming clutch will begin to transmit the twisting force. Then, the method includes rapidly reducing the outgoing clutch pressure, P-off, at a pressure which is slightly higher than the predicted outgoing relief pressure, and rapidly increasing the incoming clutch pressure P-on at a pressure that the slightly lower than the predicted incoming draft pressure. Then the method includes gradually decreasing P-off and gradually increasing P-on until the outgoing clutch slip is detected and gradually more slowly decreasing P-off and gradually and more slowly increasing P-on until the incoming clutch starts to carry the force previously carried by the outgoing clutch. Finally the method includes decreasing P-off more quickly at the reservoir pressure, and more rapidly increasing P-on at full inlet pressure.